1. Field of the Invention
This invention relates to an electrostatic display device and more particularly a chromatophore display mechanism, improved display control circuitry and cost effective methods for display production.
2. Discussion of Prior Art
Display devices based upon electrostatic attraction of a thin, insulated dielectric membrane have been disclosed in a number of prior art patents including: U.S. Pat. Nos. 3,897,997; 4,094,590; 4,105,294; 4,160,582; 4,229,075; 4,336,536; 4,468,663; 4,747,670; 4,831,371; 4,891,635; and 5,667,784. Generally these prior art devices require fabrication by assembling small mechanical parts, the very nature of which precludes cost-effective production of displays having the number of pixels typical of many display applications.
This invention bears a relation to three prior inventions by one of the inventors, Ellis D. Harris. U.S. Pat. No. 6,081,249 xe2x80x9cWRAP AROUND MEMBRANE COLOR DISPLAY DEVICExe2x80x9d describes an assembly of filament electrodes, membrane sandwiches and silicon electronics to achieve a chromatophore color display. A second patent U.S. Pat. No. 6,127,725 xe2x80x98THIN INSULATOR ON METALxe2x80x99, describes patches of silicon-on-insulator-on foil has been allowed by the U.S. Patent Office and its issue is pending. The present inventive display device utilizes features of these two inventions. The third patent bearing relation to the current disclosure is U.S. Pat. No. 6,198,512 xe2x80x98METHOD FOR COLOR IN CHROMATOPHORE DISPLAYSxe2x80x99 and describes means to transform television color signal into a form useful in a chromatophore display including a display of the type of the present invention. These above three patents are included herein by reference.
Chromatophore is the term used to designate selectable pigment elements to provide color selectivity with only ambient illumination. The classical example is the color variation in certain animals, notably a chameleon, wherein changes of color are effected by means of pigment-bearing sacs. By analogy a chromatophoric display is defined as a display wherein non self-luminous picture elements change color under electronic control and are viewable under ambient illumination.
A first primary benefit of a chromatophoric display is that the amount of power consumed is many times less than that required by current display technologies. This is especially significant for portable display devices wherein power must be supplied by a battery pack. The lower power consumption is the result of three inherent technical advantages of chromatophoric displays: 1) No power is required for transmissive illumination; 2) Each pixel does not require constant drive power to show a desired colorxe2x80x94drive power is only consumed in the instant when the color is changed; and 3) Only a fraction of the pixels are consuming drive power at any given time. An example of the last benefit would be a display used for a word processor where the only pixels requiring power are those forming the new letters as they are entered on the keyboard while the rest of the pixels remain unchanged.
A second primary benefit is that the display is viewable under very bright conditions, such as direct sunlight. The utilization of CRT, LCD or other self-luminous displays is often disappointing in bright ambient light environments because there is insufficient transmissive display illumination to create enough contrast for easy viewing. By comparison, an outdoor sign such as a billboard is highly visible in bright sunlight. A chromatophoric display combines aspects of a painting hanging on a wall or an outdoor sign viewed in reflected light with the moving features of cinema or television. Like a picture on a wall it utilizes and requires ambient illumination for viewing. Although low ambient illumination conditions may require auxiliary illumination, such auxiliary illumination need not be generated by the display itself Supplying such illumination by external means will be cost-effective relative to supplying the power needs of a self-luminous display.
A third primary benefit is that the display can be made very thin, light and flexible for many applications not possible with display technologies requiring rigid glass components.
A fourth primary benefit of chromatophoric displays is the absence of flicker which is known to induce psychosomatic distress in some individuals. Flicker is common in displays that rely on a phosphor since the phosphor for any given pixel is stimulated only once for each frame and the luminosity decays over the rest of the frame. In cinema, flicker results from the limited fraction of time that the film gate is open during a frame time. A cinema frame is mostly all on when the film gate is open and mostly all off when the film gate is closed. By contrast in a chromatophoric display, once a chromatophore color is set it remains constant and unchanged until the image requirements require a different color. Pixel brightness of a chromatophoric display does not decay during the frame time as in the case of the phosphor on a CRT display. At no time is the frame completely Black, as is the case between frames in cinema. As a consequence there is no perceivable flicker in a chromatophoric display.
A fifth primary benefit of a chromatophoric display is the ability to easily retain images. Since the flexible membrane of a chromatophore element will still retain its position when the drive signal is removed, this enables the inventive display device to hold an image for a period of time after disconnection from electronic display drivers. Display retention can be extended indefinitely with the inclusion of holding electronics including a minimum battery voltage supply. The retained display may later be recovered by connecting the display to source of electric power and synchronization.
The present inventive display device describes an innovative chromatophore geometry that makes it possible to produce high resolution displays in high volumes and cost effectively. The chromatophore geometry, display control circuitry and production methodology are applicable for both monochrome and color devicesxe2x80x94Beneficial features are inherent in both. Innovative display technologies have invariably developed first in monochromatic form and color technology has subsequently followed. When color has been available it has been preferred, both for esthetics and for the additional information that can be conveyed.
Where self-luminous displays are commonly characterized in terms of luminosity, chromatophoric displays must be characterized in terms of brightness. For the presentation of color images the inventive chromatophoric display device has the inherent capability for all pixels in any localized area to be any of the bright primary colors, Cyan, Magenta, and Yellow. This capability allows the display of highlight colors in maximum brightness. The darker primary colors of Red, Green and Blue may also be made available along with Black and White. With these eight colors many hues and chromas can be made available and human perception of color in a chromatophoric display can approximate the color resolution used extensively in multicolor printed images today.
Coloring of the chromatophores can be accomplished using ink and pigment technologies in various forms that are well known and in an advanced state of development. Pigment particle size can average 0.04 microns, with often a maximum of 0.2 microns. Colored transmissivity is optimum for the smaller particle sizes. A well-known approach to enhance color is to include fluorescence in the pigment formulation. In a typical approach a fluorescing dye is included that absorbs light in the UV and produces a fluorescence that adds to the passive pigment color.
A display device can be formed using an array of chromatophore mechanisms or elements. An array is commonly perceived in terms of rows and columns. For purposes of this present invention a more general definition is used wherein an array is considered as a grouping of elements in a general sense, including rectangular, hexagonal, circular and arbitrary arrangements of elements.
The chromatophore display can utilize electronics for image control. Transistor electronics are in a high state of development. Many hundred of thousands of transistors together with interconnectivity means are commonly fabricated on a single substrate. It is well known that transistors can be fabricated that operate at a wide range of specific voltage levels, including from only a few volts up to many tens of volts. Electronics can thus be achieved for an extended variety of chromatophore displays.
In accordance with the present invention a possible electronics module for the display comprises a substrate coated with an appropriate insulator film that in turn is coated with a film of semiconductor within which thin film transistor electronics circuits are further generated along with interconnection means. By these means islands of thin film electronics-on-insulator on a thin film substrate are achieved. Thinness, flexibility and low cost are enabled. The thin film format enables picture on the wall television as well as a computer or television displays that emulate pages of a book. In one approach particulate matter is deposited onto a substrate in a desired pattern of isolated patches by a printing or lithographic process and then fused into patches of smooth thin film. Insulator particles are first deposited onto the substrate and then fused into patches of smooth insulator film adhered to the substrate. Semiconductor particles are next deposited on the patches of insulator film and processed into electronic quality semiconductor film. This is the approach described by our patent U.S. Pat. No. 6,127,725 xe2x80x9cTHIN FILM ELECTRONICS ON INSULATOR ON METAL. The semiconductor can be any of the commonly known semiconductor material, including: silicon, germanium, gallium-arsenide or one of a number of organic semiconductor materials. TFT electronics are next generated in the semiconductor by well-known means. By this means a plurality of individual circuits are disposed in isolated patches over the extent of the chromatophore display. In subsequent steps these electronic circuit patches are interconnected and also integrated with stacks of membranes having specific optical characteristics, which then comprise the chromatophores of the display.
Utilization of thin film structures provides an inherent mechanical flexibility. The thin film assembly can be mounted by any of a number of optional methods. It could be stretched over a frame, affixed to a flat substrate, or mounted such as to be rolled up and let down typical of screens used in projection displays. Other alternate mounting means include binding one or more thin film assemblies similar to pages in a book.
The innovative chromatophore geometry of the inventive device makes it possible to use precision printing technology as the primary production process to manufacture displays instead of the complicated mechanical assembly required in previous electrostatic displays. The control circuitry, electrodes and flexible membranes of the chromatophores can be created, placed and connected through multiple printing operations. The inventive display device utilizes knowledge commonly used in printing technologies. Techniques of printing and lithography, including photolithography and microlithography are well known, having undergone technical development and improvement for decades and even centuries. Processes and materials for the utilization of photo-resists, etchants, masks, optics, pigments and inks are in a high state of development and are in common usage in industry. It is an object of this invention to utilize such techniques in fabrication of the display as a primary means to achieve low cost.
Fabrication of the chromatophore structure may be enhanced through the use of photoresist material as a temporary layer that is removed in subsequent production steps. Photoresists, as utilized in the microelectronics industry, are commonly comprised of a polymer containing an optically active additive chemical. The photoresist can be either positive of negative depending upon the action of light upon the additive. Positive resists are rendered soluble by exposure to illumination while negative resists are soluble except when rendered insoluble by exposure. A novel approach in the fabrication of the inventive display mechanism utilizes a photo resist into which two additives have been introduced. A polymer containing the two additives is formed into a desired shape and rendered insoluble by an initial exposure to a first optical wavelength that acts upon the first additive. In a later step patterning is achieved by optical activation of the second additive with a second optical wavelength followed by an etch step.
Another novel approach for fabrication of thin film sandwiches for application in the inventive mechanism incorporates features of both extrusion and casting. A mold for casting a patterned thin film is comprised of two mold halves that rotate together and an extrusion orifice through which the molded films emerge. As the film immerges it is sufficiently viscous to hold its shape temporarily. Immediately upon emerging from the orifice optical flux hardens the film.
The extrusion/casting process requires highly precise production tooling that will be manufactured with diamond turning. Diamond turning of metal is a process initially developed by the military to produce very smooth metal surfaces. The process has been utilized in the fabrication of precision metal optics. In diamond turned metal surfaces the cutting can be so fine that the surface crystal structure is undisturbed. Experiments have shown that because of lack of surface crystal disruptions a diamond turned copper surface can remain in moist air for months without losing its brightness. With careful temperature control and with steps taken to avoid mechanical disturbances, including even normal laboratory conversation, surface features can be held to within a few atomic diameters. When diamond turned tools are utilized in high volume production the high cost of the tooling will generate a minimum contribution to unit cost. With the utilization of diamond turned for mold/cast tooling, mold halves that rotate together can generate the a needed pattern for extrusion while remaining sufficiently tight where they meet on the ends as to confine the mold material. On each complete rotation of the two-piece rotary mold, a patterned thin film for one production display mechanism will be produced. Additional patterning and integration with other components will be performed in succeeding steps.
In one preferred approach a production line will comprise a plurality of mold/cast tools for the production of arrays of stacks of membrane sandwiches along with other tooling for the production of electronics modules and their integration. In other preferred approaches production tooling will be comprised of means for printing and photo-etching.
It is an object of this invention to provide an innovative chromatophoric element geometry that makes it possible to cost-effectively produce chromatophore display devices that utilize voltage positionable membranes.
It is an additional object of this invention to provide a display that is viewable in high ambient light conditions, such as bright sunlight.
It is an object of this invention to provide electrically activated chromatophores for a display device wherein each chromatophore is capable of assuming any of a selected set of colors.
It is another object of this invention to provide a high resolution, high brightness color display device wherein neither display self-luminance nor a dedicated illumination source is required, but wherein the display is viewed under ambient illumination.
It is a further object of this invention to provide a color display device wherein bright color highlights of natural objects in ambient illumination can be displayed.
It is an object of this invention to provide chromatophore flexible membranes, that have enhanced separation capabilities, flexure performance and minimized surface contact.
It is an object of this invention to provide a color chromatophore display device using an assembly of stacks of voltage positionable colored membranes whereby each chromatophore color is selectable from a palette of primary colors and wherein all chromatophores of the display are optionally able to assume any color of the primary color palette.
It is a further object of this invention to provide a color display device in thin format wherein a printed page is emulated.
It is an additional object of this invention to an optical image display device in a thin flexible format.
It is an additional object of this invention to enable xe2x80x9cPicture on the Wallxe2x80x9d television.
It is another object of this invention to provide means whereby membranes of a stack of voltage positionable membranes are positioned separately whereby mechanical forces needed are minimized.
It is yet another object of this invention to minimize the electrical drive power consumed by a color display device through control circuitry that changes only those chromatophores that need to be changed while all other chromatophores remain unchanged.
It is yet another object of this invention to provide a color display device upon which imaginal data is displayable at frame rates compatible with typical television and/or computer displays.
It is yet another object of this invention to provide a non-luminous color display whereby battery requirements for portable equipment is minimal.
It is yet another object of this invention to provide a color display device that maintains the display of a color image when the display device is disconnected from sources of power.
It is a further object of this invention to allow a stored image display to be recovered as a data stream by reconnecting the display device to sources of power and synchronization.
Other objects and attainments, together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.
A display mechanism is described having the capability of showing two or more colors using one or more flexible membranes that electrostatically switch positions between stationary electrodes of different geometry and color. Each flexible colored membrane is multi-layered and comprised of at least one conductive layer and one dielectric layer. Each membrane or stack of membranes with the adjacent electrodes serves as a single chromatophore, the color of which is altered electrically. A first colored electrode is substantially flat and parallel to a base substrate containing control circuitry. Each of a plurality of second electrodes is of a substantially rounded geometry, around which membranes wrap as determined by electronic signal. Display color is produced as electric forces separate surfaces of common color. The display is non-luminous, consumes very little power and is easily visible under normal to very bright ambient illumination. Integrated electronics provide power, signal and connectivity. A plurality of membrane sandwiches is integrated with electronics and comprises chromatophores of the display. Display control is accomplished by a chain of CMOS inverters dynamically reconfigured into a pair of sub-chains along which signals propagate in opposite directions starting from the point of initial membrane separation and ending at the point of final separation. Propagation delay enables membranes being switched between electrodes to switch separately minimizing required drive forces. Input color signal for each display chromatophore determines the sub-chain configuration that establishes element color.